This won't help the majority of users, but I have my own person mp3 server that I use that suffers from the mime-type bug. Reading this post made me realize a fix on my server side. My server serves up an M3U playlist with the correct mime-type of "audio/x-mpegurl", but firefox incorrectly uses the webpage's extension of PHP from index.php.

note: every distribution installs apache differently so the following configuration settings could be any number of places. Just search through the config files. They should all be somewhere that you can find with some searching.

I changed the extension of the PHP script that serves up the music to M3U. Then, I commented out "audio/x-mpegurl m3u" out of Apache's mime-types and added it to the list of php extensions (look for "application/x-httpd-php .php" and add a new line with ".m3u"). Then, one last step: find the line that begins "DirectoryIndex" and make sure you put "index.m3u" or something similar in the list before index.php. Restart apache and now firefox will key off of the M3U extension.

The only downside to this is if you actually store M3U playlists on your server somewhere that are served up as text files. They will be processed as PHP files from now on. There are ways around this.

I know those instructions are brief, but hopefully it will give anyone in a similar situation a pointer in the right direction. If you need help, you can e-mail me.